Owen Duffy wrote:
Jim Lux wrote in
:

...

that would be what's known as a "pier pin" base, and, as noted, it
greatly reduces the torsional load on the tower. Whether the force
causing the tower to fail is torsional, I'm not sure. Guyed towers
fail by buckling from the compressional force exerted by the guys.


The vertical elements of a tower framework should take their load in line
with the element. They are slender elements which are tied in by bracing
to prevent buckling.

It seems to me that in a typical construction where the end of that
vertical element in each section is not free to hinge, that twisting of
the section deforms the vertical element and would assist buckling if the
downwards force in the element is very large... as it is on very large
structures.

Actually, you'd look at the diagonal braces, too. On several theatrical
truss designs, the bending load limit is set by the compression buckling
of the diagonal braces, not the tension or compression of the main
tubes. A torsional load will put a bending load on the vertical main
tubes, but a longitudinal load on the diagonal braces (compression or
tension depending on which direction they go). probably also a bending
moment on the diagonal struts because they're welded joints.